Surging Idle at start up, sometimes when hot

[blazed07]

I own an 82 Blazer that I converted from the 6.2 diesel to TBI from an 87 Blazer. My problem is that I have a very rough surging idle when I first start it up (Almost like I have a "big" cam installed). The surge gets siginificanlty better as the engine warms up but you can still make out a slght surge at full temp. I also smell a slight hint of fuel in the exhaust. Aside from these issues, the Blazer drives well and never has been a problem at start up.

I have checked for vacuum leaks and have not been able to locate any leaks. I am leaning at two things at the moment: TPS or Bad Injectors.

I have performed the voltage reading test on the TPS at the closed, mid, and fully open positions on the Throttle body and everything has checked out. Can this unit be partially bad? Would you catch this on the voltage test?

The injector spray pattern is not a fully atomized spray on the driver side injector, but it is not significantly bad either.

I would appreciate it if somebody could guide me in the right direction.

 

[ryoken]

I'd be leaning towards the EGR or IAC acting up...

Throw any codes?

 

[blazed07]

I replaced the EGR valve back when we performed the engine swap. EGR circuit seems to work fine. IAC is a new unit that I replaced a while back.

I did do some adjustments with the IAC. I tried resetting what you refer to the "minimum air" and there was no change in idle quality, so I repeated the process and took the set screw back to the original setting.

I do not get any trouble codes.

 

[ryoken]

then I'd be looking at the injectors... A timing light will allow you to inspect the spray pattern... A can or 2 of Sea Foam in your tank may help clean up your injector pattern for awhile...

 

[FWP]

If you find the problem, please post up. I've been having this same intermitent problem since day 1 of my conversion, 4 years ago. It's definetely worse when the PCM is reset to default (battery disconnect, dead, etc.) Like yours, the EGR is fine, The TPS voltage is smooth (Viewed through WinALDL) I haven't installed new injectors though because they "look" good when the spray is veiwed with a timing light.

 

[blazed07]

Bad EGR the culprit?

Upon further research, it seems that my EGR valve may not be functioning as designed. I cannot test this vlave while it is installed since the diaphragm is fully encased in an outer shell. I did remove the EGR valve and put engine vacuum to it and it did not open. My questions are: Will a malfuctioning EGR valve cause a surging idle? If it is fully closed at all times, then it shouldn't cause a vacuum leak should it? Will the MAP try to compensate for a bad EGR circuit?

Any input would be greatly appreciated.

 

[ryoken]

Will a malfuctioning EGR valve cause a surging idle?

Most certainly... Thats why it was my initial responses... The other tendency is off-idle stumbling, surging...

 

[blazed07]

If the egr valve itself is not functioning properly, will it throw a trouble code? Mine is not throwing any codes and I don't have any stored codes.

Also, while I was researching prices for egr valves, i have seen more than one site that advertise valves that can "not" be tested with a vacuum pump. What's up with that?

 

[dyeager535]

EGR *should* throw a code if it's not operating correctly. MAP (TBI) setups look for the drop in manifold vacuum when the ECM applies it, so you'd get a code while cruising the freeway in a low-load condition. (throttle needs to be steady)

There are two types of EGR, one is the typical vacuum pulls it open that most are familiar with, the other is held SHUT via vacuum. (at least thats what I recall reading)

There are hundreds of GM EGR valves out there for the same make/model of vehicles, so it's possible you have one of these. This is why you might hear talk of replacing the EGR with another one that reflects the same part number only.